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1. International Journal of Engineering and Technical Research (IJETR)
ISSN: 2321-0869 (O) 2454-4698 (P), Volume-5, Issue-4, August 2016
56 www.erpublication.org

Abstract— Earlier Orthogonal frequency-division
multiplexing (OFDM) method had various disadvantages like
sensitivity to Doppler shift and frequency synchronization
problems. It had high peak to average power ratio (PAPR) and
low power efficiency and required linear transmitter circuitry.
The OFDM reduces inter Symbol interference (ISI) caused by
the delay spread of wireless channels. Therefore, it is used in
many wireless systems and is adopted by various standards.
OFDM is similar to traditional frequency-division multiplexing
(FDM) but differ in modulation and demodulation methods. The
main function is to minimize the interference or crosstalk among
the channels and symbols consisting of data streams. SCFDMA
is more advanced than OFDM. The SCFDMA system using PN
sequence the proposed part provides much better results than
the traditional OFDM. Along with this, the equalizer like
MMSE, zero forcing etc. can also be used. The PN sequences
helped in reducing the BER and also promised reliable
transmission. The equalizer is used for minimizing the error in
the signal obtained at the output. By using the equalizer and the
PN sequence, the results obtained are more efficient than the
traditional method.
Index Terms— CP, OFDM, PAPR, SCFDMA.
I. INTRODUCTION
OFDM is descriptor for orthogonal frequency division
multiplexing method used to encode the data on multiple
carrier frequencies. It is an effective technique used in many
communication systems such as audio broadcasting, DSL,
wireless networks etc. OFDM follows frequency division
multiplication method which means that data travels in the
form of multiple sub carriers on parallel channels [2]. These
sub carrier signals are modulated using existing modulation
schemes such as QAM and PSK i.e. Quadrature amplitude
modulation and Phase shift keying respectively. But
conventional modulation schemes used generate low symbol
rate in the same bandwidth. SCFDMA is an alternative here.
SCFDMA is abbreviated as single carrier frequency division
multiple access scheme. It follows the same concept as used
by the multiple access schemes like OFDM, TDMA and
FDMA in which multiple users assigned with shared
communication resource. SCFDM is same as that of OFDM
scheme except an additional step called DFT processing step
[1]. SCFDM is preferred over OFDM in the uplink
communication because it produces low PAPR value which
tends to improve power efficiency and also reduces the cost of
the power amplifier. As Single Carrier Frequency Division
Mandeep Bhardwaj, Electronics and Communication Engineering
Department, Sri Sukhmani Institute of Engineering and Technology,
Derabassi, India, +919896491977.
Sarbjeet Singh, Electronics and Communication Engineering
Department, Sri Sukhmani Institute of Engineering and Technology,
Derabassi, India, +919780939009.
Multiple Access transmits the data serially, therefore it
provides low PAPR value as compared to the OFDM system.
Its frequency offset is also less sensitive as compared to the
traditional modulation technique. SCFDMA is more robust
with respect to frequency selective fading. SCFDMA works
same as that of OFDM but has an additional step of DFT
mapper. In the SCFDMA, data mapper converts the data bits
into modulation symbols. These symbols are converted into a
block consisting of N symbols. These N symbols are
converted into the frequency domain because N-point is used
in time domain. Then the frequency mapped samples are
converted into subsets of M subcarriers. M should be greater
than N. SCFDMA has some useful properties which make
them popular such as:
• Provides less PAPR value
• Low sensitivity to carrier frequency offset
• It allows the use of low-cost power amplifiers
•
Transmitter and receiver structure of SC-FDMA:
After representation of SCFDMA, there is N point DFT at the
transmitter side and N point IDFT at the receiver side. DFT
produce frequency domain symbols that will spread over the
bandwidth. On the other side, IDFT produce time domain
channel symbols.
In this paper, SCFDMA using PN sequence technique is
proposed. Section II discusses the type of fading channels. In
section III, some existing works related to proposed approach
are discussed. Section IV deals with the methodology used to
implement the desired work. Section V and Section VI
discusses the problem formulation and proposed work
respectively. Results are shown in section VII in which the
traditional technique i.e. TFT-OFDM results are compared
with proposed technique results and paper is concluded in
section VIII.
II. FADING CHANNELS
Fading is a problem that affects the signal while travelling
over the channel. It can vary depending upon many factors
such as time, radio frequency or geographical position. A
fading channel is a type of communication channel that is
generally affected by fading. Fading can be caused by
multiple factors such as multipath propagation which causes
multipath induced fading. In the same way, shadowing may
lead to shadow fading. While travelling through media, a
signal may follow multiple paths created by reflectors present
in the environment which causes the transmitted signal to
traverse [5]. Consequently, receiver can see each signal
traversing a different path.
Performance Analysis of SCFDMA with PN
Sequence using different modulation techniques
Mandeep Bhardwaj, Sarbjeet Singh

2. Performance Analysis of SCFDMA with PN Sequence using different modulation techniques
57 www.erpublication.org
Figure 1 shows the basic block diagram of SCFDMA
In underwater acoustic communication, disturbances
occurring due to water movement may lead to distortion
which can be modeled using channel.
Depending on how rapidly the transmitted signal changes as
compared to change of the channel, Fading can been divided
into two types named as slow fading and fast fading.
Slow fading
In a slow fading channel, the channel variation rate is much
slower than the rate of change of transmitted signal. The rate
of change of channel may be assumed to be static over one or
more timing intervals. In frequency domain, this specifies that
Doppler spread of channel is much less than bandwidth of
transmitted signal in the frequency domain. This type of
fading occurs due to shadowing in which large building or hill
can destroy the path between the transmitter and receiver.
Fast fading
Fast fading deals with rate of change of channel due to
motion. In fast fading channel, rate of change of channel is
faster than rate of change of transmitted signal.
Selective Fading
It occurs due to the fact that radio signal gets partially
cancelled by itself. It is also referred as frequency selective
fading. It happens in early evening or early morning because
at that time environment conditions changes and various
layers in the ionosphere may get separated or combined which
causes fading to occur.
Selective fading is a type of fading which constantly changes
due to the cyclic disturbance sweeping through the received
audio. Thus as a result, carrier frequency of the signal will
vary leading to change in the amplitude. The coherence
bandwidth measures separation in frequency; thus two signals
will experience uncorrelated fading.
Fading Models
There are different fading models available and different in
terms of delay, gain and phase shift [5]. Some of them are:
 Nakagami fading
 Log normal shadow fading
 Rayleigh fading
 Rician fading
 Weibull fading
III. RELATED WORK
Kumar Naresh et al. This paper presents uplink and downlink
communication with the help of OFDMA and SCFDMA.
LTE i.e. Long term evolution adopted SCDFMA and used for
uplink communication. SCFDMA is also known as Discrete
Fourier Transform spread OFDM. This paper has proposed a
new technique named as Wavelet based SCFDMA to analyze
Bit error rate performance. Evaluation is performed on
several wavelets under different modulation schemes with
AWGN channel. Thus results shows that by using wavelet
transform BER is reduced and performance is better as
compared to existing approach used in SCFDMA.
Rahul Ohlan et al. This paper presents a recent trend in the
field of LTE systems which is based on the OFDM with cyclic
prefix and SCFDMA.OFDM basically used for downlink
communication whereas SCFDMA is used for uplink
communication. SCFDMA provides lower PAPR as
compared to OFDM. This paper presents some historical
techniques that had been used and also discusses survey
results.
Anurag Pandey et al. paper mainly focuses on the OFDM
system used in wireless communication due to its better data
rate and low bandwidth. Simulation has been performed to
show the results of signals over different faded channels and
to obtain optimum Bit Error Rate. This paper focuses on the
performance of the OFDM system on the basis of different
modulation schemes and Rayleigh fading channels.
Mukesh Kumar Mishra et al. This paper presents
Nakagami-m fading channels effect on OFDM system and
effected value of BER through the characteristics of function
based approach of this fading channel. BER value is
expressed in terms of confluent hyper geometric functions
known as higher transcendental function. As a result, paper
concludes that BER performance may degrade depending on
the number of channel taps as well as on the increasing value
of Nakagami-m fading parameters.
SCFDMA TransmitterData
source
N point
DFT
Channel +
Noise
Serial to
parallel
converter
Remove
cyclic
prefix
Subcarrie
r mapping
M-point
IDFT
Serial to
parallel
converter
Parallel to
serial
converter
N point
IDFT
M point
DFT then
Subcarrie
r mapping
Data
received
SCFDMA Receiver
Parallel to
serial
converter

3. International Journal of Engineering and Technical Research (IJETR)
ISSN: 2321-0869 (O) 2454-4698 (P), Volume-5, Issue-4, August 2016
58 www.erpublication.org
IV. METHODOLOGY
As problems are discussed in previous section a new approach
is proposed for work in which the methodology is divided into
two parts. One is from transmitter side and other is from
receiver side.
Transmitter Side:
1. Initially a number of data sets will be generated.
2. SNR value of the signal is to be generated in this step.
3. After generating SNR, signal is generated carrying the
information, which is to be transmitted for
communication between the transmitter and the
receiver.
4. On that generated signal different types of modulation
techniques are applied and the technique which is
best among them is chosen for the modulation of
signal.
Block diagram
Transmitter Block:
Figure 2 Block diagram of proposed technique at transmitter side
5. After modulation on the signal is performed, FFT
operation is applied on that signal.
6. After applying FFT operation on the signal, next step
is to apply IFFT operation on the received signal.
7. Now, cyclic prefix is added to the received IFFT
Signal, as cyclic prefix is generally used in
conjunction with modulation in order to retain
sinusoid properties in multipath channels.
8. Now, parallel to serial conversion of the signal is
done, so that the multiple data is transmitted at a time
and also the speed is more.
9. After adding the cyclic prefix, a PN –sequence code is
generated, by a PN-sequence code generator.
10. Finally this signal is transmitted from the transmitter.
Receiver Block:
Figure 3 Block diagram of proposed technique at Receiver side
RECEIVER SIDE:
1. On receiver side, generate a channel effect along with
the ratio of noise.
2. Then perform FFT and equalization on the signal.
3. Apply IFFT operation on the signal.
4. Perform demodulation on the signal.
5. Remove cyclic prefix from the received signal.
6. Now compare the transmitted signal with the received
signal and calculate the error in the signal.
V. PROBLEM FORMULATION
Orthogonal frequency-division multiplexing (OFDM)
diminishes the effect of inter-symbol interference (ISI).
Therefore, it is used in many wireless systems and adopted by
various standards. OFDM is much similar to traditional
Define no. of data sets.
Define SNR value
Generate Signal
Perform serial to parallel
conversion and modulation
Apply FFT operation on the
signal
Now, perform IFFT operation
on the signal
Add the cyclic prefix to the
signal.
A P-N sequence code is
generated by the PN sequence
generator.
Parallel to serial conversion of
the signal
Finally transmit the signal.
Channel effect along with noise
Apply FFT on the parallel data along with
equalization
Demodulation of signal and
remove cyclic prefix
Calculate BER
Apply IFFT on the signal

4. Performance Analysis of SCFDMA with PN Sequence using different modulation techniques
59 www.erpublication.org
frequency-division multiplexing (FDM) in many ways. They
can only be differentiated on the basis of modulation and
demodulation methods. The main function is to minimize the
interference or crosstalk among the channels and symbols
consisting of data streams. Less significance is placed on
perfecting the channels. Still some of the problems exist, like
High peak to average power ratio having amplitude variations
which resembles noise like appearance. Also OFDM has low
RF amplifier efficiency. The basic reason is that it
accommodates the large amplitude variations. These factors
leads amplifier to operate with a low efficiency level and its
sensitivity to carrier offset and drift also increases. Single
carrier systems are less sensitive as compared OFDM.
VI. PROPOSED SYSTEM
The traditional OFDM technique suffers from various
problems such as frequency synchronization. It is highly
sensitive to Doppler shift. Also it has high peak to average
power ratio (PAPR), requiring linear transmitter circuitry,
which leads to low power efficiency. Further, there is loss of
efficiency caused by cyclic/guard interval. To overcome these
limitations, it was advised to use various coding algorithms
like PN sequence codes which improves efficiency or other
multiple access technique.
By introducing the PN sequence code with the OFDM system
the modified part gives much better results than the traditional
OFDM. Along with this the equalizer like MMSE, zero
forcing etc. can also be used. The PN sequences helped
reducing the BER and also promised reliable transmission.
The equalizer are used for the minimizing the error in the
signal that is obtained at the output. By using the equalizer
and the PN sequence the results obtained are more efficient
than the traditional method.
Objectives:
 To replace the traditional OFDM technique in reduction
of BER
 To Introduce the encoding approach in proposed
communication system to enhance the performance of the
system
 To introduce the PN sequence and equalizer to improve
the performance of the OFDM system.
 Calculation of performance parameters of proposed work
and analysis
 Design and develop the work in the software name
MATLAB
VII. SIMULATION AND RESULTS
To implement SCFDMA, we used information stream of 4096
bits having block size of 512 bits. The cyclic prefix of length
52 for each subcarrier is used. The n-point FFT and IFFT is
used at the transmitter and receiver where n denotes the size of
block. The PN sequence generator generates 8-bit random
sequence. The signal is processed using generated PN
sequence and different modulation techniques such as BPSK,
QPSK and QAM-16. The modulated 4512 bit data stream is
transmitted serially to implement SCFDMA. The value of
m-factor for nakagami-m channel is 0.5 and omega equal to 2
is used. For simulation, 16 randomly selected values are
picked and shown on the graph.
Figure 4 Figure 5
Figure 6
Figure 4, 5, 6 shows the graph which represents the Power
Spectral Density Ratio of BPSK, QPSK and QAM-16.
Figure 7 Figure 8
Figure 9 Figure 10
Figure 7, 8, 9, 10 represent the graph of BER i.e. Bit Error
Rate of STBC-TFT-OFDM, BER of SC-FDMA with
BPSK,QPSK and QAM modulation techniques respectively.
Figure 11 Figure 12
Figure 11 shows the graph which compares the PSNR of
SC-FDMA signal w.r.t various modulation techniques like
QAM, QPSK, and BPSK. The graph shows that the PSNR

5. International Journal of Engineering and Technical Research (IJETR)
ISSN: 2321-0869 (O) 2454-4698 (P), Volume-5, Issue-4, August 2016
60 www.erpublication.org
value of SCFDMA (QAM) is efficient as compare to other
modulation techniques. Figure 12 shows the comparison of
BER of traditional OFDM with proposed SCFDMA system.
Graph shows that the proposed system provides better BER
results as compared to the existing system. Further, QAM
qualifies as the best modulation technique among others.
VIII. CONCLUSION AND FUTURE SCOPE
From results it is concluded that proposed method is best and
efficient than the traditional method. There are a large number
of techniques available in order to apply modulation on
SC-FDMA signals. It is observed that the QAM 16 is the best
approach to reduce the BER of the signal as compare to other
modulation techniques.
As a future scope further enhancement can be done in this
method by using trending technique for transmission of
signal. Along with the SCFDMA technique, there can also be
other techniques that can be used to produce quality retain
signal at the receiving end. Furthermore, techniques can be
developed that may simple in manipulation than the proposed
technique.
ACKNOWLEDGMENT
I would like to thank Mr. Sarbjeet Singh, who had been
guiding throughout to complete the work successfully on
“Performance Analysis of SCFDMA with PN Sequence using
different modulation techniques".
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Mandeep Bhardwaj Bachelor of Engineering in Electronics and
Communication, M.Tech Scholar at Sri Sukhmani Institute of Engineering
and Technology, Derabassi, Punjab, India.
Sarbjeet Singh Masters of Technology in Electronics and
Communication, Assistant Professor, Sri Sukhmani Institute of Engineering
and Technology, Derabassi, Punjab, India.